Portable devices for radiation detection and radiation measurement are used in many different fields to check personnel, equipment and facilities for radioactive contamination, or to detect and measure external or ambient ionizing radiation. Common instruments for these purposes comprise Geiger-Müller tubes and scintillation counters. A Geiger-Müller tube comprises a chamber filled with an inert gas, in which free electrons are produced in response to incident ionizing radiation. The electrons propagate in an electrical field and trigger an electric discharge avalanche which may then be detected at the anode. A scintillation counter, in contrast, comprises a scintillator crystal in which photons are generated in response to incident radiation. A sensitive photomultiplier tube is coupled to the scintillator, where electrons are generated by means of the photoelectric effect and are then amplified into an avalanche of electrons that can be read out and detected.
However, both detection techniques require the drifting of charged particles over relatively long distances, and are hence sensitive to external magnetic fields. For this reason, these devices are not well-suited to provide reliable measurement results in environments with high magnetic fields, such as in the spatial vicinity of research or medical particle accelerators. Similar problems are encountered when performing radiation surveys at medical magneto-resonance imaging (MRI) operated in multimodality with positron emission tomography (PET) instrumentation, or magnetic separation in industrial mineral processing.
A radiation dose meter for measuring a radiation dose in an external magnetic field is described in International Patent Publication WO 2012/023855 A1, and comprises an alignment unit capable of precisely aligning the radiation dose meter in the external magnetic field so that the path of the charged particles inside the radiation dose meter is substantially parallel to the direction of the external magnetic field and no deviation occurs. However, the device requires a precise detection of the spatial orientation of the external magnetic field, and the alignment unit additionally adds to the bulkiness and complexity of the device.
What is needed is a simple and compact radiation detection device that can be operated reliably even in intense and varying magnetic fields.